1. Field of the Invention
The present invention relates to a communication controlling method which is suitably used where there is a need for adjusting the amounts or levels of communication resources allocated to each communication session. The present invention also is concerned with a communication controlling apparatus suitable for carrying out such a communication controlling method.
2. Description of the Related Art
Nowadays, various studies and research are being conducted in order to implement real-time communications in wide-area networks. One of the measures proposed through such studies and research, which is now expected to be promising, employs a protocol which is referred to as "resource reservation protocol" which reserves, in advance of the commencement of a communication, the resource which is necessary for the communication to be achieved, so as to ensure high degree of QoS (Quality of Service). The term "resource" is used hereto mean, for example, CPU (Central Processing Unit) processing time, network bands, data buffer capacity, or the like.
In the case of the internet community, there are two types of protocols which are noted as being usable in Internet Draft, which is a phase prior to the phase of RFC (Request for Comments) which describes the protocol specifications. One of these two types of protocol is the RSVP (Resource Reservation Protocol) mentioned above, while the other is ST-2 (Internet Stream Protocol, Version 2).
It is highly desirable that the use of such a resource reservation protocol makes efficient use of the resources which are limited in amounts. There are some resource reservation protocols which are intended to meet this requirement. In such a protocol, a mechanism is employed which permits a dynamic change in QoS of a specified communication session or sessions. In the following description, this type of control will be referred to as "Dynamic QoS Control". In most cases, the Dynamic QoS control is triggered by a communication end point.
FIG. 1 schematically shows how the conventional D.Q.C is performed. A plurality of nodes (host computers) are indicated by ellipses. A Dynamic QoS Control demand is issued from an end entity (host or node) which is marked as "source 1" to a destination node which is marked as "destination 2". Thus, in the conventional Dynamic QoS Control mechanism, the control of QoS is normally conducted explicitly by the entity which is the communication end point.
Meanwhile, studies and research are also being undertaken for developing technology which are to be used in wide-area network for the purpose of enabling transfer of continuous media data, e.g., video and audio data which require real-time reproduction, as well as transfer of data which undergoes a very severe restrictions in regard to time.
It is to be noted, however, various problems or difficulties are encountered in completing communications, when resources necessary for communications are allocated exclusively to a certain communication session. For instance, it is not a rare case that a communication session which has reserved the resources constantly make full use of such reserved resources.
More specifically, when a communication session reserves a resource, the session designates the resource amount with parameters which are determined based on the maximum presumable rate of data transfer. However, the amount of data normally transferred is much smaller than the maximum data transfer. Consequently, there remains a considerable amount of resource which has been reserved but not usually used. This undesirably leads to an ineffective use of the limited resource.